A toner which contains an erasable, i.e., reversible, coloring material which includes a coloring compound and a developer which interacts with the coloring compound and in which the color is erased, i.e., rendered substantially invisible to the human eye by later heating, is known. By using such a toner, the color image formed using the toner on a recording medium such as paper is erased by heat, and it is thus possible to reuse the recording medium on which the image was formed. Such a technique is considerably effective, from the viewpoint of environmental protection and economic efficiency by reducing the amount of the recording medium used by enabling direct recycling of the recording media for additional image formation thereon.
Such, a toner in which the color is erased by heating is a manufactured by a dry method or a wet method; however, when a kneading and grinding method which is a dry method is used, since when the coloring material described above is melted and kneaded under high shear and under high temperature when mixed with a binder resin, the coloring compound and the color developing material become separately dispersed in the binder resin and the reactions therebetween are resultantly inhibited, and therefore a decrease in the color development density, i.e., the density of the color in the image, of the toner occurs.
In contrast, in a wet method such as an emulsion aggregation method in which toner component fine particles such as the erasable coloring material and the binder resin are aggregated and fused in water to produce toner particles, the coloring compound and the color developing material are not significantly separately dispersed in the resulting toner, and therefore it is possible to prevent a decrease in the color development density in the resulting image.